In a typical substrate processing apparatus for performing a process, for example, an etching, a substrate such as a semiconductor wafer, a transfer device (a transfer robot), in which a transfer pick for supporting the substrate is provided on a leading end of a transfer arm, which extends and rotates in specific directions and vertically moves without restriction, is used to transfer the substrate into a processing chamber. Typically, a plurality of contact members, each of which is made of elastomer, is provided on a wafer support surface of the transfer pick. The contact members are brought into contact with the substrate to support the substrate thereon.
The contact members of the transfer pick are made of elastomer because the position of the substrate, placed on the transfer pick, can be prevented from undesirably being misaligned out of the correct position due to the adhesive force of the elastomer. However, as the substrates are repeatedly transferred, foreign particles or deposits from processed substrates get adhered to the contact members, thereby decreasing the adhesive force of the contact members made of elastomer. Given the decrease in the adhesive force, the position of the substrate on the transfer pick is made to be easily misaligned out of the correct position. As a result, the accuracy of the transfer operation is reduced, and this results in defective products. Moreover, the substrate may be dropped during the transfer operation. Furthermore, when transferring the substrate by the contact members of the transfer pick having foreign particles adhered to the contact members, the foreign particles are transferred and adhered to the rear surface of the substrate when the transfer pick is brought into close contact with the rear surface of the substrate, thus causing a problem of particle contamination for the substrates.
To avoid such a problem, an operator, in the prior art, is required to periodically clean the contact members of the transfer pick. However, by manually cleaning the contact members, additional operation time is consumed and the stoppage of the substrate processing apparatus during the cleaning process cannot be avoided. Therefore, the cleaning operation cannot be performed as many time as desired, and the above-mentioned likelihood of misalignment of substrate caused by a reduction in the adhesive force of the transfer pick still remains.
In an effort to overcome the above problems, there has been proposed a method, in which foreign particles that exist in the processing space are charged with electricity by a particle electric charging unit, and an electric field having the same polarity as that of the particles is created around a transfer arm by an electric field creating device so that the foreign particles are prevented from being adhered to a semiconductor substrate (for example, see Patent Reference 1: Japanese Patent Laid-open Publication No. 2005-116823 (e.g., paragraph 0057)).
The technique of Patent Reference 1 prevents particles from being adhered to a semiconductor substrate using the method of creating an electric field for providing repulsive force with respect to the particles around the transfer arm, but it does not consider the removal of foreign particles, which cause the substrate to be misaligned out of the correct position on the transfer pick, from the contact members of the transfer pick.